Plant Disease

Plant diseases can be caused by a range of different pathogens. Identifying diseases helps to limit the effects of pathogens and prevent the spread of disease across an entire crop. This can be carried out either in the field or in the lab.

The table below shows some common symptoms of plant diseases.

Stunted growthIt can be caused by pests, such as mealybugs. However, it can often be caused by mineral deficiencies or poor environmental conditions.
Spots on leavesSpots can appear on leaves due to rose black spot, which is a fungal disease.
Areas of decayThe most common causes of decay in plants are bacteria and fungi. For example, root rot can be caused by fungal infections and a lack of oxygen.
GrowthsCrown gall is a bacterial disease that causes plant tissues to grow abnormally.
Malformed stems or leavesAn infection can hinder the development of stems and leaves. For example, this is caused by ash dieback, which is a fungal disease.
Presence of pestsPlant pests interfere with plant growth and cause damage. If pests are identified on a plant, it is likely that the plant is infected.
DiscolourationFactors that interfere with the plant’s chlorophyll production can lead to discolouration.

For example, a magnesium deficiency can cause discolouration because magnesium is required for chlorophyll production. The tobacco mosaic virus can also cause discolouration.

Remember: Factors other than the disease may cause these symptoms and the symptoms of different plant infections can overlap. So alternative techniques may be required:

  • Gardeners often refer to gardening manuals or use websites to identify plant diseases. They often include a picture of the plant, showing what it should look like.
  • The infected plants can be taken to a laboratory to undergo DNA analysis, which will help to identify the pathogen.
  • Using testing kits that contain monoclonal antibodies to identify the pathogen

Mineral Ion Deficiencies

Mineral ionPurpose in plantDeficiency
MagnesiumUsed to make chlorophyll in leaves, which is needed for photosynthesisLess chlorophyll causes leaves to turn yellow (chlorosis) and leads to stunted growth
NitrateProvides nitrogen for the production of amino acids, which are needed to make proteinsA lack of nitrates reduces the number of chloroplasts in leaves. This causes leaves to turn a pale green and yellow colour.

The reduction in chloroplasts also leads to stunted growth

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